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Compensation Expense Associated with Performance Units (Detail) - Performance Units Awards - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
2020    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Stock-based compensation expense associated with Performance Units $ 69  
2019    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Stock-based compensation expense associated with Performance Units 830 $ 830
2018    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Stock-based compensation expense associated with Performance Units $ 667 667
2017    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Stock-based compensation expense associated with Performance Units   $ 482